Exploiting starfish in pyrolysis for the enhanced generation of syngas and CO2-looping agent

Abstract

Starfish (Asterina pectinifera) has been considered a major invasive species with no natural predators in the marine ecosystem. They can destroy the natural marine system when the population growth is too high, suggesting the development of a sustainable way to dispose of starfish. Therefore, this study offers a sustainable thermo-chemical platform for the direct conversion of starfish waste into value-added syngas (CO and H2) and biochar. Major gaseous products from the starfish pyrolysis under both the N2 and CO2 conditions were H2, CH4 and CO. H2 and CH4 were likely ascribed to dehydrogenation and C–C bond scission of starfish, while CO formation was from homogeneous reaction of CO2 with volatile organic matters from starfish pyrolysis. Under the N2 environment, CO2 liberated from the thermolysis of CaCO3, a major constituent of starfish, contributed to formation of CO. Such the mechanistic effectiveness of CO2 was confirmed by starfish pyrolysis under the CO2 environment. However, the effectiveness of CO2 on gas phase homogeneous reaction with volatile compounds was not fully activated during thermolysis in one-stage pyrolysis due to source depletion at high temperature. To improve the effectiveness of CO2, additional thermal energy was applied through two-stage pyrolysis (isothermal running at 600 °C). The homogeneous reaction of CO2 with volatile compounds liberated from starfish pyrolysis with additional thermal energy highly contributed to enhanced formation of CO. In line with the substantial generation of CO in the presence of CO2, high concentration of CO2 also contributed to more pore creation. These observations indicate that the construction of CO2-looping system from starfish pyrolysis would become a sustainable way to produce syngas and porous biochar.